1. Field of the Invention
The present invention relates to a device for extracting damaged bolts, nuts, screws and the like, that cannot be removed with ordinary tools.
2. Description of the Background Art
The extraction of bolts and nuts with rounded or broken heads using a hammer and an ordinary chisel is generally known to persons involved in repairing machinery and the like.
Typically, a chisel is placed against the side or edge of a bolt and a hammer is used to drive the cutting edge of the chisel into the bolt to impart rotational force. If the bolt is rusted or torqued to a high degree the chisel will cut into the bolt too far and will simply slice away the edge of the bolt and send the cut material flying. Mechanics often try to avoid this by switching to a chisel with a dull or blunted edge before the cut is too deep. This maneuver is sometimes successful if the bolt is not overly tight. However, the blunted edge of this chisel will spread the kerf made by the original chisel and eventually spread away and slice off the outer edge of the bolt creating a potentially dangerous missile if rotation of the bolt is not accomplished. If the broken fragment leaves a bench or shoulder on the bolt, the mechanic might try holding a punch against the shoulder in an attempt to achieve rotation without further damage to the bolt head or nut. Holding a flat punch against the shoulder and coordinating hammer blows to impart rotational force requires considerable skill, and not all mechanics possess this skill. Frequently, too much attention is paid to one end of the chisel and it is not uncommon to strike the hand holding the chisel with the hammer, or allow the working end of the chisel to slip off the bolt.
Bolts that have broken off at or near the surface of the threaded body are also a common problem encountered by mechanics repairing machinery. To avoid further drilling and using a screw extractor the repairman will frequently try hammering a small chisel or punch into the outer edge of the broken bolt at an angle that will impart some rotational force. However, if the bolt is rusted or tightly threaded the chisel or punch will penetrate deeply into the bolt and expand the material of the bolt tightly against the tapped threads. Further hammering will only cause additional expansion of the bolt and may damage the tapped threads in the body.
In view of the above problem and in the interest of safety and expediency, a specialized tool is needed for removal of damaged bolts and nuts.